1. Technical Field
The present invention relates to a vibrating reed, an angular velocity sensor, an electronic device, and a moving object.
2. Related Art
Generally, vibrating reeds have been used in angular velocity sensors (gyro sensors) (FIG. 1 of JP-A-2012-098091 and JP-A-2012-112748). In FIG. 1 of JP-A-2012-098091, for example, when an angular velocity motion about the Y axis is applied to a vibrating reed extending in the Y direction, a drive unit that is subjected to an in-plane vibration in the X direction in the X-Y plane is then changed to be subjected to an out-of-plane vibration in the Z axis direction (the thickness direction of the vibrating reed) by the action of the Carioles force. The component of the force in the Z direction causes a detection unit to move. By such a component of the force, an electric field is generated in the X direction in the detection unit by the piezoelectric effect. Based on the electric field, the detection unit outputs an output signal; hence, the angular velocity is detected.
As a vibrating reed used in a gyro sensor, a technology is proposed in which a groove (an interference prevention portion) that is open to a side surface of a detection unit and in which the depth direction thereof is set in the X direction is provided in the detection unit (FIG. 4 of JP-A-2001-221638). The groove is arranged to prevent the electrical coupling interference between a pluralities of electrodes provided on outside surfaces of the detection unit without including electrodes on the inside surface or the groove bottom thereof. This suppresses the occurrence of leakage voltage.
As another vibrating reed used in a gyro sensor, a technology is proposed in which a step portion is formed on side surfaces of a detection unit, and the distance in the X direction between a pair of electrodes formed on both side surfaces of the detection unit is narrowed so as to improve the efficiency of the electric field (FIG. 3 of JP-A-2011-141266).
When the area of electrodes arranged in a detection unit is narrowed along with the miniaturization of gyro sensors, the electric field in the X direction generated in response to the component of the force becomes weaker; and thus, the detection sensitivity decreases. It is considered to enlarge the area of the electrodes by providing a groove that is open to a main surface of the detection unit unlike in FIG. 4 of JP-A-2001-221638 and FIG. 3 of JP-A-2011-141266. However, electric charge loss may apparently occur when the position of formation of electrodes is not considered in a case where the detection unit of a vibrating reed vibrates along the thickness direction thereof such as in gyro sensors.